<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>负边距对浮动元素的影响</title>
  <style>
    *{padding;margin:0;}
    #box{
        width:280px;
        border:1px solid black;
        overflow:hidden;
    }
    #box .float{
        width:100px;
        height:100px;
        float:left;
    }
    #box .float:nth-child(1){
        background:red;
    }
    #box .float:nth-child(2){
        background:yellow;
    }
    #box .float:nth-child(3){
        background:blue;
        margin-left:-20px;
    }
  </style>
</head>
<body>
  <div id="box">
    <div class="float">1</div>
    <div class="float">2</div>
    <div class="float">3</div>
  </div>
</body>
</html>